Method of providing a lead wire seal

ABSTRACT

A method for creating an improved seal between oxide-coated lead wires and the glass envelope of an evacuated electron discharge tube. A group of lead wires are disposed in a suitable array and then surrounded by a glass blank. As the lead wires and glass are heated to soften the glass preparatory to the formation of a seal, the heat causes an increased buildup of oxide upon the side of the lead wires remote from the surface of the glass. A reducing flame is then applied to the inner surfaces of the lead wires to diminish the thickness of the undesired oxide buildup. The softened glass is then forced about the lead wires, dissolving a portion of the remaining oxide to produce a hermetic seal.

Hamon [451 Jan. 2, 1973 METHOD OF PROVIDING A LEAD WIRE SEAL inventor:Richard Eugene Hamon, Syracuse, NY. 13209 1 Assignee: General ElectricCompany, Syracuse,N.Y.

Filed: Jan. 4, 1971 Appl. No.: 103,755

US. 0|. ..65/59, 65/32, 65/154 Int. Cl ..c03 29/00 Field of Search..65/59, 138, 147, 154, 32

References Cited UNITED STATES PATENTS Primary Examiner-Robert L.Lindsay, Jr.

Assistant Examiner-Kenneth Schor Attorney-Frank L. Neuhauser, Oscar B.Waddell, Joseph B. Forman, Marvin Snyder and W. J. Shanley, Jr.

[57] ABSTRACT A method for creating an improved seal betweenoxide-coated lead wires and the glass envelope of an evacuated electrondischarge tube. A group of lead wires are disposed in a suitable arrayand then surrounded by a glass blank. As the lead wires and glass areheated to soften the glass preparatory to the formation of a seal, theheat causes an increased buildup of oxide upon the side, of the leadwires remote from the surface of the glass. A reducing flame isthen'applied to the inner surfaces of the lead wires to diminish thethickness of the undesired oxide buildup. The softened glass is thenforced about the lead wires, dissolving a portion of the remaining oxideto produce a hermetic seal.

6 Claims, 4 Drawing Figures PATENTEDJAH 2 I973 3.708.272

mvnu'ron RICHARD E. HAMW ATTOR N EY METHOD OF PROVIDING A LEAD WIRE SEALBACKGROUND OF THE INVENTION The present invention relates to themanufacture of hermetically sealed envelopes for electrical dischargedevices, and, more particularly, to a method for providing an improvedseal between a metallic conductive member and a glass envelope.

The problem of providing a strong, reliable seal between metallic leadsand the surrounding glass of an electron discharge tube envelope haslong plagued the industry. Early problems included an incompatabilitybetween the thermal coefficients of expansion of the lead wire materialand of the surrounding glass. Eventually lead wire materials wereformulated which had a compatable coefficient of expansion; however,providing a reliable seal between the lead wire and the glass remained aproblem. One means of solving this problem was to provide a portion ofthe lead wire with a metallic cladding, the oxide of which is soluble inthe envelope glass. During the manufacturing process, the oxidizedsurfaces of the lead wires are surrounded by molten glass and the outerportion of the oxidized metal dissolves into the glass to form acontinuous bond from the underlying metal cladding to the glassenvelope.

In one widely used method embodying the above technique, a plurality oflead wires are disposed in a desired configuration, such as a circulararray. A preformed glass blank is placed about the upstanding lead wiressuch that the inner surface of the glass blank is in close proximity toeach of the lead wires. Heat is then applied to the assembly in order toheat the lead wires and soften the glass so that the glass can bepressed about the lead wires and into a desired configuration. Thenow-softened glass blank and associated lead wires are compressed in amold, causing the glass to assume a desired configuration, flowing aboutthe lead wires in sealing relationship.

A persistent problem occurring in this mode of manufacture has been anasymmetrical or nonuniform buildup of metal oxide upon the lead wiresduring the heating operation. As the lead wires and glass blank areheated, the lead wire cladding tends to oxidize, further causing anincrease in the thickness of the oxide layer. As the glass blanksoftens, the inner surface bellies inwardly and contacts the upstandinglead wires so that the oxide on the side of each lead wire adjacent theglass blank dissolves into the glass, while the oxide at the opposite orremote side of the wire continues to increase in thickness. When thesoftened glass is pressed, the oxide upon the remote side of the wireordinarily is not dissolved adequately, with the result that a thicklayer of porous undissolved oxide is left between the lead wire and thesurrounding glass. Prolonged heating of the assembly would cause thethickened oxide to be dissolved into the glass to the desired extent,but during this period the thinner oxide layer would be completelydissolved leaving a physically weak interface between the glass and thenascent cladding metal.

Another approach is to conduct the manufacturing process in anoxygen-free or a reducing environment. Producing and maintaining such anenvironment, however, is undesirably expensive and further limits accessto and supervision of the process. It will thus be seen that it would bedesirable to provide an economical method by which an unevenaccumulation of oxide upon lead wire surfaces is prevented.

It is therefore an object of the present invention to provide a methodfor equalizing oxide thickness about a lead wire prior to sealing itwithin a glass envelope material.

SUMMARY OF THE INVENTION Briefly stated, in accordance with one aspectof the invention a plurality of lead wires are arrayed in a patterncorresponding to a desired final lead position. An apertured glass blankis placed about the arrayed lead wires such that each wire is in closeproximity to the inner surface of the blank. Heat is applied to theassembly for heating the lead wires to form oxide layers thereon and forraising the temperature of the glass to a point at which the glasssoftens and is capable of being worked. The softened glass flowsinwardly and contacts the outer surfaces of the lead wires at theregions adjacent to the glass, dissolving further oxide formed thereat.Oxidation continues to build up, however, at the regions of the leadwire remote from the glass, resulting in formation of a nonuniform oxidelayer about each lead wire. A reducing hydrogen flame is then played onthe lead wires such that it impinges most directly upon the regions ofthe oxide layers remote from the glass blank, the flame serving toreduce the accumulated oxide thereat, diminishing its thickness to adimension which is substantially the same as that of the oxide adjacentthe glass blank. The softened glass blank is then pressed by means of asuitable mold such that the glass envelops the peripheries of the leadwires, and assumes a desired configuration.

BRIEF DESCRIPTION OF THE DRAWING While the specification concludes withclaims particularly pointing out and distinctly claiming the subjectmatter which is regarded as the invention, it is believed that theinvention will be better understood from the following description ofthe preferred embodiment taken in connection with the accompanyingdrawing in which:

FIG. I is a drawing of a cathode ray tube envelope showing lead wiresextending through a stern assembly thereof;

FIG. 2 is a view of the lead assembly of FIG. 1 during manufacture,before a pressing operation has been completed;

FIG. 3 is an enlarged cross-sectional view of a lead wire having anasymmetrical oxide coating thereon; and

FIG. 4 is an end view of a complete stem assembly.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. 1 there is shown a cathoderay tube 10 including a gun 11 mounted therein and connected to aplurality of lead wires 12. The lead wires extend through a glass wafer13 and are hermetically sealed therein to prevent the leakage of airinto the evacuated area within tube 10. A tubulation 14 extends throughwafer 13 and has the distal end thereof sealed. The tubulation, leadwires and wafer are permanently united to comprise a stem assembly. Aprotective cap 15 may be placed over tubulation l4 and wafer 13 to addphysical support and to prevent breakage.

Each of the lead wires 12 advantageously comprises three sections. Afirst section 18 extending within cathode ray tube may be made from asteel alloy having the desired physical and electrical characteristics.Similarly, an outer end 16 may be made from a similar alloy having therequisite conductivity and having the strength and rigidity to form aserviceable exterior contact. A third, central portion 17 of the leadwire comprises almost all of that portion of the wire which is envelopedby the glass of wafer 13. Ordinarily, the alloys suitable for sections16 and 18 of the lead wire have thermal coefficients of expansion whichdiffer from that of the glass, preventing the creation of a sealtherebetween which will withstand substantial variations in temperature.For that reason, the central section 17 of the lead wires may be made ofa suitable metal, such as Dumet. Dumet, a metal familiar to thoseconversant with the art and commonly used for glassenclosed leadportions, has the requisite electrical characteristics for use as a leadwire material, and,

further, has a thermal coefficient of expansion in the radial directionwhich is substantially the same as that of glass. Each end of the Dumetsection 17 is welded to the adjacent lead wire sections 16 and 18. Thejunction between middle section 17 and the inner end of lead wiresection 18 is enclosed by a glass fillet 19 which extends just farenough to cover the joint. Similarly, the junction between the Dumetportion 17 and the inner end of lead wire section 16 is covered by aglass button 20 which arises from the wafer. The lead wire thusconstituted includes extending portions having the necessary strengthand support, while most of the portion embedded in the glass wafer has athermal coefficient of expansion compatible with thatof the glass forproviding a reliable seal.

In FIG. 2 one step of a popular method of manufacturing the stemassembly is depicted. The desired number of lead wires 12 are disposedin an appropriate pattern and held by a clamping device (not shown).While a total of 12 lead wires are shown, arranged in a circle, it willbe apparent that more or fewer lead wires could be utilized and disposedin various other configurations. An annular glass blank 21 is slippedover the lead wire array such that each lead wire is in close proximityto the inner periphery of the blank. An exhaust tubulation 14 is placedwithin the lead wire array and oriented generally parallel with the leadwires. Heat is then applied to the assembly preparatory to pressing theglass blank 21 for causing the softened glass to flow about the leadwires 12 and exhaust tubulation 14.

In order to provide a hermetic seal between the lead wire and thesurrounding glass the middle portion 17 of each lead wire is clad with acoating of a metal such as copper, the outer surface of which is allowedto oxidize. As is well known, such oxides readily dissolve in moltenglass to complete a bond which is essentially continuous from thesurface of the lead wire into the glass itself. Since metals oxidize inthe atmosphere as temperature is raised, as the assembly shown in FIG. 2is heated the thickness of the oxide coating of lead ;wires 12increases. However, as the glass blank softens it deforms in such amanner as to allow its inner the blank such that a relatively thin layerof oxide above copper coating 25 is maintained. At the remote orinnermost side of each lead wire, corresponding in the present instanceto those surfaces directed radially inward of the circular array, oxidebuildup continues unmitigated by the presence of the glass solvent.

The resulting cross-sectional configuration is illustrated inexaggerated form in FIG. 3. The circular cross section of the middleelement 17 of a lead wire is maintained during the heating process, butthe thickness of the copper oxide 22 which is disposed about coppercladding 25 varies nonuniformly about the lead wire. That side of thelead wire in contact with glass blank 21 maintains a desirably thindepth of oxide layer at region 23. However, diametrically opposite fromthe edge of glass blank 21 the thickness of oxide at region 24 continuesto increase. As the oxide thickness increases the oxide becomes porousand, if then enveloped by molten glass, will ordinarily afford a porouschannel disposed axially along one side of the lead wire through whichthe atmosphere can enter the interior of an evacuated envelope. It ispossible to dissolve most of the excess oxide at region 24 by the simpleexpedient of maintaining the enveloping glass at a high temperature foran extended period of time. When this is done, however, the molten glasssoon dissolves all of the thinner oxide layer at region 23 so that theglass abuts either nascent cladding material or the inner Dumet portionof the lead wire, providing an unacceptably weak interface.

In FIG. 4, there is shown an end view of the stem assembly after thepressing operation. The molten glass blank has been pressed into adisk-like element 13, surrounding lead wires 12 and enveloping theperiphery of exhaust tubulation 14. Further, the surfaces of the moldingdevice (not shown) used to press the glass blank are advantageouslyprovided with recesses registering about each of the lead wires 12 suchthat buttons 20 are formed about each lead wire as it arises from thedisk. The assembly may then be inserted into a suitable envelope and theouter periphery of the disk 13 hermetically sealed to the envelope byglass-to-glass fusing. The interior of the envelope is then evacuatedthrough exhaust tubulation 14, after which the tubulation is sealed.

It will be recognized that a layer of thick, porous oxide extendingaxially along the middle section of leads 12 will allow air to passthrough the stem assembly and invade the evacuated envelope. In the pastit has been the practice to regard porosity resulting from unduly thickoxide as being a defect inherent in the above-described manufacturingprocess. Stem assemblies were commonly manufactured in numbers in excessof that needed, then tested and defective ones destroyed, the unusableassemblies being considered simply as an added factor in the cost ofproduction.

The present method comprises an inexpensive process by which thedetrimental oxide buildup may be easily diminished without interruptingthe manufacturing cycle. In practicing the inventive process, the leadwires 12 are arrayed in the normal position, as shown in FIG. 2. Exhausttubulation 14 is secured in an appropriate position and an annular glassblank 21 disposed about the lead wires. Heat is then applied for heatingthe lead wires and softening the glass blank preparatory to the normalpressing operation. After a suitable temperature has been attained bythe assembly but before the pressing operation a reducing agent such asa reducing flame, preferably constituted by a jet of hydrogen, isapplied to lead wires 12 such that the flame impinges primarily upon theinner surfaces of the lead wires. By directing the jet in this manner itwill be seen that the reducing flame directly contacts the oxide coatingat the region of maximum thickness 24. While the reducing agent could beconstituted in other ways, the flame of a gas such as hydrogen serves tomaintain the requisite temperature and support necessary reductionprocess. As will be recognized by those skilled in the art the hydrogenflame serves to reduce the oxide. To put it another way, the applicationof the hydrogen or other reducing element essentially extracts theoxygen from the oxide to leave only the parent metal. In accomplishingthis, the volume of the oxide is depleted and so the thickness of theoxide layer is deceased. After a suitable time the oxide layer at region24 has diminished to a thickness which is substantially the same as thethickness of region 23, resulting in a substantially uniformly thickoxide layer about each respective lead wire. At this time, applicationof the reducing agent is terminated and the pressing operationcommences. A suitable die or mold is applied to the glass blank andassociated exhaust tubulation 14 and lead wires 12, causing the glass toflow inwardly of the lead wires, surrounding and sealing the lead wiresand the exhaust tubulation. As the molten glass surrounds the lead wires12 it encounters the portion of which is uncovered by glass oxide layer22 thereabout, at which time the formerly uncovered portion of oxidebegins to dissolve into the glass. Since the oxide is now distributedevenly about the periphery of the lead wire 12 the assembly may beallowed to cool at a rate suitable for allowing nearly all of the oxidelayer to dissolve into the glass. Since the oxide layer is ofasubstantially constant thickness the dissolving takes place at anessentially even rate about the periphery of each lead wire. It is thuspossible to ascertain a point in time at which the oxide has dissolvedadequately, without leaving thick, porous oxide areas.

While for purposes of illustration the process has been described usingcopper oxide and hydrogen for the bonding and reducing agentsrespectively, it will be appreciated that other oxides and reducingagents may be utilized in the process without substantially affectingthe basic nature thereof. Further, while round lead wires have beenrepresented the process is applicable to leads having variousconfigurations, and it is therefore contemplated that othermodifications or applications will occur to those skilled in the art. Itis thus intended that the appended claims shall cover all suchmodifications and applications as do not depart from the true spirit andscope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. The method of effecting a seal between glass and a lead wire havingan oxidizable outer surface, including the steps of? disposing apreformed blank of said glass adjacent to said surface along a portionof said surface;

heating the juxtaposed glass and lead wire to soften the glass and forman oxide layer about said wire,

said oxide layer being thicker on the region'of said wire remote fromthe glass than on the region of said wire adjacent the glass;

directing a reducing agent onto said oxide layer on the region of saidwire remote from the glass to I diminish the thickness of said oxidelayer thereat to the approximate thickness of said oxide layer on theregion of said wire adjacent said glass, thereby rendering said oxidelayer substantially uniformly thick about said wire; and

causing the softened glass to surround said wire and dissolve a portionof said oxide layer about said wire.

2. An improved method for effecting a hermetic seal between glass and aplurality of lead wires to extend therethrough, said lead wires havingoxidizable outer surfaces, comprising the steps of:

arranging said lead wires in a desired pattern within the opening of anapertured blank of said glass, each of said lead wires being in closeproximity to said glass; heating the juxtaposed glass and lead wires tosoften the glass and form an oxide layer about each of said wires, eachsaid oxide layer being thicker on the region of each respective wireremote from the glass than on the region of said wire adjacent theglass; directing a reducing agent onto each said oxide layer on theregion of said wire remote from the glass to diminish the thickness ofthe oxide layer thereat [:o the approximate thickness of the oxide layeron the region of said wire adjacent said glass and thereby render theoxide layer substantially uniformly thick about said wire; and

causing the softened glass to surround each of said wires and dissolve aportion of each said oxide layer respectively disposed thereon.

3. The method as set forth in claim 2, wherein said reducing agent is ahydrogen flame.

4. An improved method for effecting a hermetic seal between glass and aplurality of lead wires to extend therethrough, a portion of each one ofsaid lead wires being fabricated of conductive material having anoxidizable metallic coating disposed on the outer surface thereof, saidconductive material having substantially the same thermal coefficient ofexpansion in the radial direction as that of said glass, said methodcomprising the steps of:

arranging said plurality of lead wires in a desired pattern within theopening of an apertured blank of said glass such that a portion of eachsaid coating is in close proximity to the glass;

heating the juxtaposed glass and lead wires to soften the glass and forman oxide layer about each said coating, each said oxide layer beingthicker on the region of its respective coating remote from the glassthan on the region of its respective coating adjacent the glass;

allowing the softened glass to contact and cover a portion of each saidoxide layer and dissolve said layer thereunder to a relatively thindepth above said respective coating;

directing a reducing flame upon the thicker region of each said oxidelayer to decrease the thickness of each said oxide layer thereat; and

molding the softened glass about the remaining uncovered portion of eachsaid oxide layer to dis-- solve said layer thereunder substantially tosaid relatively thin depth above said respective coating and therebyform a hermetic seal with each of said lead wires.

2. An improved method for effecting a hermetic seal between glass and aplurality of lead wires to extend therethrough, said lead wires havingoxidizable outer surfaces, comprising the steps of: arranging said leadwires in a desired pattern within the opening of an apertured blank ofsaid glass, each of said lead wires being in close proximity to saidglass; heating the juxtaposed glass and lead wires to soften the glassand form an oxide layer about each of said wires, each said oxide layerbeing thicker on the region of each respective wire remote from theglass than on the region of said wire adjacent the glass; directing areducing agent onto each said oxide layer on the region of said wireremote from the glass to diminish the thickness of the oxide layerthereat to the approximate thickness of the oxide layer on the region ofsaid wire adjacent said glass and thereby render the oxide layersubstantially uniformly thick about said wire; and causing the softenedglass to surround each of said wires and dissolve a portion of each saidoxide layer respectively disposed thereon.
 3. The method as set forth inclaim 2, wherein said reducing agent is a hydrogen flame.
 4. An improvedmethod for effecting a hermetic seal between glass and a plurality oflead wires to extend therethroUgh, a portion of each one of said leadwires being fabricated of conductive material having an oxidizablemetallic coating disposed on the outer surface thereof, said conductivematerial having substantially the same thermal coefficient of expansionin the radial direction as that of said glass, said method comprisingthe steps of: arranging said plurality of lead wires in a desiredpattern within the opening of an apertured blank of said glass such thata portion of each said coating is in close proximity to the glass;heating the juxtaposed glass and lead wires to soften the glass and forman oxide layer about each said coating, each said oxide layer beingthicker on the region of its respective coating remote from the glassthan on the region of its respective coating adjacent the glass;allowing the softened glass to contact and cover a portion of each saidoxide layer and dissolve said layer thereunder to a relatively thindepth above said respective coating; directing a reducing flame upon thethicker region of each said oxide layer to decrease the thickness ofeach said oxide layer thereat; and molding the softened glass about theremaining uncovered portion of each said oxide layer to dissolve saidlayer thereunder substantially to said relatively thin depth above saidrespective coating and thereby form a hermetic seal with each of saidlead wires.
 5. The process set forth in claim 4, wherein said reducingflame is a hydrogen flame.
 6. The process set forth in claim 5, whereinsaid oxidizable metallic coating is comprised of copper.